Willstrop was 83 and had been battling cancer.
Based at Pontefract Squash & Leisure Club, Willstrop helped both his son, James, and Lee Beachill rise to become World No 1 in the men’s game.
But he also proved a magnet for ambitious squash players from around the world, who were drawn to his Yorkshire base to learn and improve their game.
In a statement released on Tuesday, his son James, said: “It has been a difficult few weeks for him, in which time he certainly made up for the fact that he hasn’t visited a GP for 50 years as the C-word took hold.
“As is to be expected he was stoic, witty and opinionated all the way to the line. Everybody knew who was in charge!
“The beautiful carers and nurses that looked after Malc over the past couple of months have shown us something very special about the human spirit and we would like to express our love and gratitude to them here.”
Beachill, from Huddersfield, who went on to become the Professional Squash Association’s Chief Operating Officer, said Willstrop had been a big part of his life since the age of seven.
“Malc was much more than my coach for 25 years and a close friend for a further 10,” he said.
“He was someone who I could speak to about anything, someone I could ask for anything and someone who I trusted implicitly. Malc was the most loyal person you could ever wish to meet, and I will miss our conversations greatly.
“I am proud of what we achieved together, and although Malc would never take any credit – 'it is always about the player!' – I can safely say I would never have achieved what I did without him by my side, and for that I owe him everything. The squash world has lost a truly special person.”
Elsewhere, the PSA added: “Malcolm has mentored & inspired countless players across the world of squash and his passing will leave a big hole in the squash community. Rest in peace, Malcolm.”
Willstrop is survived by James, James’s partner, Vanessa, and his grandsons, Logan and Bram.